You junked the injection pump by taking the top off of it. The pistons are set in the bores for the correct fuel delivery.
Kind of like going out and cutting your electric transformer pole down when all that need done was a fuse replaced.
You should have loosened the injector lines and cranked/pulled it around until all the air was out of the system. With the injection lines tight they will not bleed very fast just pulling it around.
That $800 may just be a starting point. You may have really damaged the pump beyond repair. Good luck you are going to need it.